Welcome to the forum, nice drop on the numbers , now the trick is to keep them around that level without shooting up too high again.

Have you tried anything other than/or in addition to meds to stimulate his appetite? Does he have a favorite food/treat he goes nuts for? Freeze dried treats such as Pure Bites is a healthy option that will not affect the phos levels too much, especially the chicken, this can be crumbled & sprinkled on the food to entice him to try it.

Sitting beside him while he eats may also help, hand feeding if necessary - the most important thing at this point is getting him to eat.

Is he nauseous? Licking his lips often? Standing over the water bowl but not drinking?

What is his energy level like? Still want to go for walks?

For the fluid supplies have you checked the prices at your local pharmacy/walmart?

Have a look around for a local medical supply company, one that supplies hospitals/pharmacies/doctors offices etc some will do in house sales when they know the purpose or if you have a prescription from your vet. That is where I purchased my fluid supplies from, the company I used allowed off sales for CRF clients and is listed on the site below under Canada, of course it would be cheaper for you to find a company in your area to save on the cost of shipping/hassle of customs importing across country borders.

Be sure that if you do purchase fluids online that you get the exact same solution as from your vet, there are many types of fluids that are used for subq injections and some have additives that may not be appropriate for your dogs' situation.

The Blue Hub needles would be 23g you can verify this by looking at the side of the hub it should be printed right on it. 23g is a good size for a dog of that size, though you could go to a slightly bigger size if you feel this is flowing to slow for his liking (if he squirms too much, gets restless during the treatment cuz it takes too long), I was using a 21g Ultra Thin Wall from Terumo on my cat.

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